hmmm... what do you mean by a primitive group?
So, do you reject anything and any word that is not explicitly written in scripture? That is your interpretation of scripture right?
Primitive Christianity is a movement that attempts to practice the exact “faith once delivered to the Saints” (Jude 1:3). That is to say, the doctrines and practices that Jesus conveyed to the first apostles without changes, embellishment or contamination by people who thought they knew better.
Such Christians observe the same Sabbath that Jesus observed, they keep the same Holy Days that Jesus kept and no others and they do His commandments fully, not adding to them (Revelation 22:14). They would also utterly reject the observation of any syncretic days such as Halloween or Xmas.
see for example the book by Alan Knight, Primitive Christianity in Crisis.
Sorry, but since I have good friends who go to The Church of God, I knew they believed in the Trinity. See below
Declaration of Faith
The Church of God believes the whole Bible to be completely and equally inspired and that it is the written Word of God. The Church of God has adopted the following Declaration of Faith as its standard and official expression of its doctrine.
We Believe:
In the verbal inspiration of the Bible.
************************
In one God eternally existing in three persons; namely, the Father, Son, and Holy Ghost.
************************
That Jesus Christ is the only begotten Son of the Father, conceived of the Holy Ghost, and born of the Virgin Mary. That Jesus was crucified, buried, and raised from the dead. That He ascended to heaven and is today at the right hand of the Father as the Intercessor.
That all have sinned and come short of the glory of God and that repentance is commanded of God for all and necessary for forgiveness of sins.
That justification, regeneration, and the new birth are wrought by faith in the blood of Jesus Christ.
In sanctification subsequent to the new birth, through faith in the blood of Christ; through the Word, and by the Holy Ghost.
Holiness to be God’s standard of living for His people.
In the baptism with the Holy Ghost subsequent to a clean heart.
In speaking with other tongues as the Spirit gives utterance and that it is the initial evidence of the baptism of the Holy Ghost.
In water baptism by immersion, and all who repent should be baptized in the name of the Father, and of the Son, and of the Holy Ghost.
Divine healing is provided for all in the atonement.
In the Lord’s Supper and washing of the saints’ feet.
In the premillennial second coming of Jesus. First, to resurrect the righteous dead and to catch away the living saints to Him in the air. Second, to reign on the earth a thousand years.
In the bodily resurrection; eternal life for the righteous, and eternal punishment for the wicked.
f
http://www.churchofgod.org/index.php/pages/declairation-of-faith